The present invention relates to a viewfinder of the single-lens reflex type for cameras such as VTR cameras, for example, and a method of adjusting such a viewfinder for eliminating any deviation of a viewfinder image from an optical axis of the viewfinder and any inclination of the viewfinder image in order to achieve complete agreement between the viewfinder image and an image focused on an image pickup device in the camera.
Viewfinders in cameras are required to give the operator a viewfinder image which agrees as accurately as possible with an image on a film or image pickup device in the camera. Twin-lens reflex cameras fail to produce such correct viewfinder images since the viewfinder image is formed by a ray of light coming through a viewfinder lens which is positionally different from the lens which focuses images on films or image pickup devices.
Many cameras in use today incorporate a single-lens reflex type viewfinder into which a portion of light passing through a main lens of the camera is guided so that images on the viewfinder and image pickup or focusing surface are identical with each other. Video tape recording (VTR) cameras include such single-lens reflex type viewfinders for the reasons that images on the viewfinder and the image pickup device are liable to be out of agreement as their size is relatively small, especially as compared with the size of images in 35 mm still cameras, and monitoring televisions are used while taking pictures to find any disagreement between a viewfinder image and a corresponding picked-up image.
Known single-lens reflex type viewfinders are however subject to machining and assembling errors which result in deviations of viewfinder images from an optical axis of the viewfinder or in inclined viewfinder images. Prior arrangements for correcting such image deviation or inclination include adjustment screws to incline a viewfinder mirror and prism, which however require a tedious and time-consuming trial-and-error procedure in order to get a proper viewfinder image.